This invention relates to an adjustable velocity fuse for a hydraulic line and, more particularly, to a fuse that can be adjusted while the hydraulic line is operational and without disturbing the hydraulic circuit.
Velocity fuses which are also known as excess flow protectors, safety valves and hydraulic circuit breakers, have been used for years to close or block flow in hydraulic lines if excess flow occurs. This may happen when a hose ruptures or when there is a free flow condition in the hydraulic circuit.
On most current fuses, the fuse point or shutoff flow rate is established by an orifice within the fuse. Changing the orifice size changes the fuse point flow rate. The orifice is drilled to the correct size by the manufacturer. To change the orifice size and thereby the fuse point, the valve must be disassembled and the orifice size changed.
On many machines which use a fuse in a hydraulic circuit, it is desirable to adjust the fuse point to match the machine characteristics and/or the operating conditions. This is difficult and impractical with current fuses because it would require a disassembly of the fuse, redrilling or replacing the orifice and reassembly each time an adjustment is needed.
A second problem with current fuses is premature closing or fusing. "Short duration" surges of flow in a hydraulic circuit are common. It is desirable for the fuse to permit "short duration" surges, but fuse if the surge persists.
A third problem with current fuses is the variation in fusing point as the fluid viscosity changes. Changes in fluid temperature change the fluid viscosity and likewise the fuse point of the fuse. For example, a manufacturer may set the fuse point at a fluid temperature of 100.degree. F. The machine operator may start the machine at minus 20.degree. F. As the machine warms up, it may operate at 200.degree. F. The fuse point could be grossly different at each of the three temperatures.
The invention provides a solution to the foregoing problems through the provision of an adjustable poppet valve assembly resiliently urged away from a fixed seat. A guide is provided which effectively masks all of the assembly except for the poppet valve head whereby the inventive fuse is sensitive to pressure differentials across the poppet valve head and seat to overcome the resilient bias. By the same token, however, the limited amount of surface area of the moving parts minimizes the fuse's sensitivity to changes in fluid viscosity. The fuse is further equipped with a dash pot chamber to prevent premature closing as on short duration surges. Further, and most importantly, an external adjustment is provided to change the position of the poppet valve assembly while the fluid is flowing through the fuse and without disturbing the hydraulic system.
Other advantages and objects of the invention may be seen in the details of the ensuing specification.